Local Anesthetics Flashcards
Mechanism of action of local anesthetics?
Drug binds Na+ channels when they open, blocking them. This doesn’t allow for propagation of nerve signals.
What is the most important consideration in nerve blocks?
Size of nerve. Small fibers are affected before larger fibers.
What types of nerve fibers are the smallest?
Sensory pain and postganglionic sympathetic nerurons
What nerve fibers are blocked first, myelinated or unmyelinated nerves?
Myelinated.
Faster the neuronal firing rate -> greater blocking effect
What nerve fibers have the highest firing rate?
Sensory pain fibers
T/F? Any dose of local anesthetic that causes loss of pain will causes vasodilation.
True
Why can’t anesthetic be given orally?
1st pass effect destroys oral agents.
How is topical absorption of local anesthetic?
Poor.
Better on broken skin or in special formulations such as EMLA, LMX-4 cream, Zingo powder, or Lidoderm patch
What has a longer t1/2, amides or esters?
Esters - t1/2 is minutes long
Esters are metabolized by?
Plasma esterases (cholinesterase)
Amides are metabolized by?
Liver amidases
Do amides or esters have higher allergenicity?
Ester
Most common adverse effect of lidocaine?
Lightheadedness/drowsiness
What can occur when local anesthetics reach levels over 7.5 mcg/mL?
Convulsions followed by CNS depression leading to death by respiratory failure
What adverse effect is associated with large doses of prilocaine via metabolite production?
Methemoglobinemia
